This invention relates to a drying-pressing machine of the type in which the washing to be pressed makes its way between a rotating, internally heated, pressing cylinder and endless belts which are in contact with the external surface of the cylinder over the greater part of its circumference.
Such drying-pressing machines are used commonly in establishments within which a large quantity of washing is processed on a daily basis. By way of examples which are in no way limitative one could mention hospitals, clinics, retirement homes, restaurants etc.
In drying-pressing machines fitted with a rotating, internally heated pressing cylinder, the pressing cylinder is constituted by a metal sheet the extremities of which rest on rollers supported on the machine chassis. In large size machines, the diameter of the pressing cylinder goes up to about 600 mm, for a length of 4 or 5 meters.
Taking into account the large diameter of the pressing cylinder which is fitted to drying-pressing machines of this type, this cylinder is normally fabricated from a flat sheet which is bent and whose adjacent edges are finally welded along a generator.
In existing pressing cylinders fabricated according to this technique, the weld which extends over the whole length of the cylinder constitutes an area of stress, causing deformation of the cylinder under the effect of the variations in temperature which arise when the machine is being used. In order to limit these deformations, one is driven to use steel, in the form of relatively thick sheet (about 4 to 6 mm depending on the diameter).
Furthermore, the humid environment in which the pressing cylinder is permanently to be found, poses problems of oxidation for the ordinary steel commonly used, notably when the machine is in a saline environment as is the case on the coast. This corrosion phenomenon is even more difficult to control when the temperatures to which the cylinder is heated do not allow it to be protected, for example, by a resin, when the machine is in operation.
Taking account of the large dimensions of the pressing cylinder, the relatively thick nature of the sheet steel in which it is formed gives the cylinder a large mass, which is not without consequences for the sizing of the structures of the machine that are used to support this cylinder.
Hence the high mass of the pressing cylinder requires that metal rollers are used, generally cast iron or steel, in order to support the cylinder at each of its extremities. These metal rollers, which must be of relatively large size, are fixed onto spindles which are rotatably mounted, using ball bearings, in parts of the chassis of the machine situated beyond the extremities of the cylinder. In certain cases, the rollers are mounted on cantilevers which requires each to be supported by means of two ball bearings of large size. In other cases, the rollers are mounted on common spindles which extend over the entire length of the machine and which also lead to the use of large size ball bearings. In all cases, this layout, in itself relatively expensive, requires in addition that the chassis is provided with a reinforced structure, capable of bearing the high forces which are applied to it. These cumulative characteristics are therefore translated into extra costs which are not negligible for drying-pressing machines designed in this way.
In addition the metal to metal contact between the steel of the pressing cylinder and the steel or the cast iron of the rollers translates itself at the same time into both relatively unpleasant noise for the user and premature wear of the rollers and the end areas of the cylinder in contact with these rollers.
The high mass of the pressing cylinder of current machines also has the consequence of high thermal inertia, which is detrimental to good matching of the machine to the nature of the washing being pressed.